The large near-field intensity gradients afforded by plasmonic nanotweezers have been an area of increasing interest, particularly in the field of lab-on-a-chip (LOC) devices. Indeed, the attributes of amplified optical forces and flexibility in shaping the optical potential energy landscape are well-suited for trapping nanoparticles, investigating colloidal dynamics, and manipulating biological species. In addition, arrays of gold bowtie nanoantennas (BNAs) are capable of yielding optical trapping efficiencies that are twenty times greater than conventional optical trapping, permitting the use of low input power densities.
In recent years, applications of plasmonic nanoantennas have focused on optical trapping, basic studies in thermoplasmonics, solar energy harvesting and biosensing. The particularly attractive feature of metal nanoantennas is their ability to concentrate light into subwavelength regions with local field enhancements as high as 104. Generally, nanoantennas are fabricated bound to a dielectric substrate, with their geometry and functionality remaining fixed after fabrication. Still, there has been a recent push to place the nanoantennas on pillars, thereby elevating them above the substrate, in order to increase the field/sensitivity enhancement for sensor applications. Indeed, it has been shown that an array of Si pillar-supported nanoantennas could enhance the signal for surface enhanced Raman scattering. To date, however, known fabrication techniques have limited pillar materials to metals or to a semiconductor substrate material, typically silicon, which is not optically transparent.
Thus, innovative techniques are needed in order to provide advantageously for a wide array of applications of plasmonic nanoantennas with insulating pillars. Such techniques are described below.
Superplastic deformation of silica has been induced by electron beams in nanowires, as reported by Zheng et al., “Electron-beam assisted superplastic shaping of nanoscale amorphous silica,” Nat. Commun., 1:24, pp. 1-8 (2010) (hereinafter, “Zheng 2010”). Organized superplastic deformation of an array structure, which has never been suggested, would be tremendously advantageous in the context of methods and application discussed below.
A background review of prior art lab-on-a-chip nano architectures was provided by Kim, “Joining plasmonics with microfluidics: from convenience to inevitability,” Lab Chip, vol. 12, pp. 3611-23 (2012) (hereinafter “Kim 2012”), which publication is incorporated herein by reference.
The following prior art publications provide further background teachings relating to optical trapping by antenna arrays that are directly deposited onto a substrate. Both publications are incorporated herein by reference:                Roxworthy, et al., “Application of Plasmonic Bowtie Nanoantenna Arrays for Optical Trapping, Stacking, and Sorting, Nano Lett., pp. 796-802 (2012); and        Roxworthy, et al., “Plasmonic nanotweezers: strong influence of adhesion layer and nanostructure orientation on trapping performance,” Opt. Exp., pp. 9591-9603 (2012).        